In vitro seed germination and seedling growth of an endangered epiphytic orchid, Dendrobium officinale, endemic to China using mycorrhizal fungi (Tulasnella sp.)

To date, tropical orchids appear to commonly associate with mycorrhizal fungi assignable to Tulasnella (Basidiomycota) for their seed germination and developmental needs in situ. In this study, two Tulasnella strains (JC-02 and JC-05) isolated from roots of an endangered species, Dendrobium nobile Lindl (Orchidaceae) collected from Yunnan province in China, were identified using the nuclear ribosomal internal transcribed spacer (ITS) and 5.8S rDNA sequences. Seed germination and plant growth were evaluated up to 11 weeks and 7 weeks after interaction with Tulasnella fungi, respectively. The results revealed that the two isolates could promote seeds germination up to stage 5 after sowing for 11 weeks, and the rates of germination were 98.47% and 99.05%, respectively, higher than that of control (81.05%). Without fungi, seed development was arrested at stage 2. After inoculating Tulasnella isolate to seedlings for 49 days, it was found that mycelium formed pelotons in the cortical cells of roots in the form of intact and degenerate pelotons. Significant differences were detected between the control group and the experimental group treated with Tulasnella isolates in dry weight and fresh weight of plants respectively. The study firstly demonstrated that two different strains of Tulasnella vary in their ability to facilitate germination/development of D. officinale in vitro.